1. Field of the Invention
The present invention relates to compounds capable of forming stable fluorescent uranium complexes, methods for synthesizing thereof, fluorescent probes for detecting uranium formed of such compounds, and methods for analyzing uranium using such probes.
2. Description of the Related Art
Uranium compounds may be present in liquid and solid wastes generated from nuclear facilities such as nuclear power plants and research facilities using radioactive materials. If uranium is present in the liquid and solid wastes, its concentration must be determined before these wastes are disposed of. Traditionally, uranium present in the wastes has been determined by mass spectrometry after isolated from the wastes by using complicated isolation procedures such as ion-exchange and solvent extraction. The detection limit of uranium by mass-spectrometry has been in the order of parts-per-trillion (ppt) to parts-per-quadrillion (ppq) (i.e., 10−12 to 10−10M). However, equipment used for mass-spectrometry is quite expensive and susceptible to contamination by a variety of radionuclides present in the wastes.
On the other hand, a method for qualitatively and quantitatively analyzing a metal ion present in a sample solution has been developed in which a metal detection fluorescent probe having a “ligand-spacer-fluorophore” structure is mixed with a metal-containing sample to form a fluorescent metal complex, which is subsequently separated by gel electrophoresis for qualitatively and quantitatively analyzing the metal present in the sample (See, for example, Patent Articles 1 (JP 2009-150650 A) and 2 (JP 2009-168450 A)). Specifically, the following ligands are used in this approach: 2-(4-fluorescein-thiocarbamyl-aminobenzyl)-ethylenediamine tetraacetic acid (FTC-ABEDTA),
2-(4-fluorescein-thiocarbamyl-aminobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (FTC-ABDOTA),
2-(4-fluorescein-thiocarbamyl-aminobenzyl)-diethylenetriamine pentaacetic acid (F1C-ABDTPA), and
N-[(R)-2-amino-3-(p-fluorescein-thiocarbamyl-phenyl)propyl]-trans-(S,S)-cyclohexan e-1,2-diamine-N,N′,N′,N″,N″-pentaacetic acid (FTC-CHX-A″-DTPA). The inventors of the present invention have used each of these ligands to form a fluorescent uranium complex with UO22+ ion present in a sample, which was then subjected to electrophoresis for qualitatively and quantitatively analyzing uranium present in the sample. However, these fluorescent uranium complexes are highly unstable that they quickly decompose into the probe and the metal, making it a challenge to qualitatively and quantitatively analyze uranium present in samples.
Meanwhile, an attempt has been made to provide compounds that are capable of forming stable complexes with UO22+ ion (See, Non-Patent Article 1 (Diane A. Blake et al, Biosensors & Bioelectronics 16, 2001, p 799-809)).